Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. Processed substrates, e.g., semiconductor wafers, are often inspected after processing to determine whether there are any defects. An inspection tool may scan a substrate and collect images of selected portions of the substrate that are suspected to contain defects. Such images are sometimes referred to as patch images. After an inspection scan has completed a user can review the patch images to determine whether defects are present.
It is within this context that embodiments of the present invention arise.